U.S. patent number 3,966,383 [Application Number 05/537,195] was granted by the patent office on 1976-06-29 for apparatus for embossing film.
This patent grant is currently assigned to Ethyl Corporation. Invention is credited to Francis H. Bussey, Jr., James K. Rutherfoord.
United States Patent |
3,966,383 |
Bussey, Jr. , et
al. |
June 29, 1976 |
Apparatus for embossing film
Abstract
An apparatus for vacuum embossing sheet thermoplastic material
which utilizes an endless, seamless structure as the embossing
surface. A sheet of heat-softened thermoplastic film is passed over
an embossing screen, the embossing screen being supported by a
support roll, a drive roll and two seal rolls. A vacuum is applied
to the screen between the seal rolls to pull the film into contact
with the screen thereby producing an embossed pattern on the film
corresponding to the outer surface of the screen. After the film is
removed from the endless, seamless screen the film is cooled to set
the pattern in the film. The process produces an embossed film
which has high strength, low surface gloss or light reflectance,
and a deep embossed pattern.
Inventors: |
Bussey, Jr.; Francis H.
(Rosedale, IN), Rutherfoord; James K. (Terre Haute, IN) |
Assignee: |
Ethyl Corporation (Richmond,
VA)
|
Family
ID: |
24141622 |
Appl.
No.: |
05/537,195 |
Filed: |
December 30, 1974 |
Current U.S.
Class: |
425/388; 264/555;
264/284; 425/194 |
Current CPC
Class: |
B29C
59/06 (20130101) |
Current International
Class: |
B29C
59/02 (20060101); B29C 59/06 (20060101); B29C
017/00 () |
Field of
Search: |
;425/194,126,224,378,384,388,385,466,326R ;264/92,284 ;74/241 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Baldwin; Robert D.
Assistant Examiner: Charvat; Robert J.
Attorney, Agent or Firm: Johnson; Donald L. Sieberth; John
F. Ray; David L.
Claims
What is claimed is:
1. In an apparatus for vacuum embossing sheet material, the
combination comprising:
a. a pair of spaced apart, generally parallel end plates;
b. a pair of spaced apart, parallel, hollow rollers rotatably
connected to said end plates, one of said rollers having heating
means connected thereto, the other of said rollers cooling means
connected thereto;
c. an endless, seamless, flexible, porous screen fitted over said
rollers connecting said rollers together to cause one roller to
rotate when the other roller rotates;
d. drive means connected to one of said rollers to rotate said
roller and advance said screen;
e. a vacuum assembly connected to said end plates and engaging a
portion of the underside of said screen that extends between said
rollers, said assembly positioned between said pair of rollers and
partially inside said screen so that the portion of said screen
passing over said roller having heating means connected thereto
contacts said vacuum assembly before contacting said roller having
cooling means connected thereto, said assembly including:
i. a vacuum manifold means connected to said end plates;
ii. seal roll retainer means connected to said manifold means;
iii. a pair of spaced apart cylindrical seal rolls rotatably
supported by said seal roll retainer means and said manifold means,
each of said seal rolls rotatably contacting the underside of said
screen;
iv. two movably mounted end seal members connected to said end
plates by adjusting means adjacent each end of said seal rolls,
said end seal members making sliding, sealing contact with said
manifold means, both of said seal rolls and the underside of said
screen to provide a vacuum chamber underlying that portion of said
screen lying between the lines of contact made on the underside of
said screen by said seal rolls.
2. In the apparatus of claim 1 wherein said heating means includes
means for supplying a flow of fluid through the hollow portion of
said roller, said fluid having a temperature above the temperature
of said sheet material prior to embossing.
3. In the apparatus of claim 2 wherein said cooling means includes
means for supplying a flow of fluid through the hollow portion of
said drive roller, said fluid having a temperature below the
temperature of said sheet material after the embossing.
4. In the apparatus of claim 2 including means for positioning said
screen on said pair of roller means while said apparatus is
embossing said sheet material to maintain said screen between the
respective ends of said pair of rollers.
5. In the apparatus of claim 4 wherein said means for positioning
said screen includes electric eye means for determining the
position of said screen and hydraulic cylinder means connected to
said electric eye means for moving one of said roller means.
6. In the apparatus of claim 2 wherein said pair of cylindrical
seal rolls are constructed from a fluorine-containing polymeric
material.
7. In the apparatus of claim 6 wherein said fluorine-containing
polymeric material is Teflon.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for producing
embossed thermoplastic sheet material utilizing a vacuum embossing
method and apparatus with an endless, seamless screen as the
embossing surface, the screen being supported by a support roll, a
drive roll, and two seal rolls.
Embossed plastic film or sheet material has come into widespread
use in many fields. One particularly large scale use of embossed
thermoplastic sheet material is that of disposable articles such as
hospital pads and drapes, wearing apparel and disposable diapers.
Embossed film is also finding increased use in the packaging field,
for example, as bags or overwraps for articles such as clothing and
for shopping bags. In order to fulfill the requirements established
by the end use of embossed film, is is desirable that the film have
suitable properties for handling by fabricating machines,
particularly those used for the manufacture of disposable articles,
e.g., disposable diapers, sheets, pillow cases, drapes, raincoats,
etc. In many cases it is important that the embossed thermoplastic
film be soft and flexible and have the proper pattern and embossed
depth in order to provide the desired "hand" or clothlike feel for
the thermoplastic embossed material. Additionally, for many uses it
is desired that the embossed thermoplastic material have as low a
surface gloss as possible in order to simulate woven clothlike
fabrics. Further, embossed thermoplastic materials must meet
minimum physical specifications which are necessary in order that
the films be handled in high speed, automatic fabricating machines,
i.e., they should have suitable modulus, tensile strength, and
impact strength.
Heretofore, embossed thermoplastic films such as polyethylene,
polypropylene, polybutene-1, polyvinyl chloride and other flexible
thermoplastic thin films have been made by various methods. One
method is to extrude the thermoplastic film from a conventional
slot die onto a continuously moving, smooth, cool, casting surface,
e.g., a chill roll. The engraved pattern may be applied to the
chill roll and the film pressed to the roll while in the amorphous
or molten stage by press rolls. Alternatively, the chill roll may
be smooth and the desired pattern in the film may be pressed into
the film on the chill roll by means of an engraved and machined
embossing roll which is pressed against the film and the chill roll
to impress the pattern into the film as it is cooled on the chill
roll.
Another technique used is to produce engraved rollers and to
provide a heated, moving strip of film for engagement by the nip of
the rollers, one of which carries the embossing pattern.
Embossed film has been prepared to a very limited extent by the use
of vacuum embossing processes. Heretofore, it has been difficult to
economically produce vacuum embossed film which has the
characteristics and properties of film produced by the more
conventional high pressure embossing processes. In one process for
producing vacuum embossed film an endless belt made of a wire mesh
which is butt welded to produce the endless belt is utilized. One
embodiment is carried over a vacuum box, and heated film is applied
thereto to impress the pattern of the screen on the heated film. In
another embodiment the endless, butt welded screen is mounted on a
cylindrical drum having a foraminous surface, and vacuum is applied
to the hollow drum to pull the heated film into contact with the
wire screen. However, the belts have a welded joint mark which
marks the embossed film once during each revolution of the belt.
Thus, the film is suitable only for use in limited applications
wherein the pattern can be cut into sections and used to avoid the
joint mark produced by brazing or welding the ends of the metal
screen together.
Other processes used in vacuum embossing film utilize perforated
vacuum embossing cylinders which carry an outer layer of a porous
substance, such as metallic mesh, fiberglass, embossed paper or
woven fabric materials as the outer embossing surface thereon. The
perforated cylinders carry on their outer surface the sized sleeve
which is either butt jointed and/or lap jointed and thus produces a
transverse mark on the thermoplastic embossed film as it is carried
over the joint in the sleeve covering. It has been suggested to
reweave the fabric together; however, it has been found that this
is an extremely tedious and expensive operation and cannot be
commercially accomplished to produce a wide variety of rolls from
fabric materials.
From the foregoing it can be seen that the previously utilized
processes and apparatuses for vacuum embossing film suffer from
numerous disadvantages which either increase the cost of vacuum
embossed film and/or produce vacuum embossed film which does not
have properties equivalent to that of film embossed by the pressure
embossing method. Previously used processes and apparatuses for
vacuum embossing film have suffered from the inability to produce
long, continuous lengths of vacuum embossed film without having
transverse marks across the film at periodic intervals equal to the
length of the emobssing belt and/or the circumference of the
screens which are used to cover the embossing cylinder.
Additionally, many of the processes and apparatuses used heretofore
for vacuum embossing film do not produce clear, distinct, sharp
patterns having the desired "hand" or feel which is comparable to
pressure embossed film. Further, many of the films produced by
vacuum embossing have been found to be very deficient in physical
properties to equivalent embossed films, i.e., they have a low
modulus, low tear strength, poor impact strength and nonuniform
roll contours when rolled into large size rolls for shipment.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus
for producing vacuum embossed thermoplastic film.
It is a further object of the present invention to provide
apparatus for producing vacuum embossed thermoplastic film having
enhanced physical properties.
It is a still further object of the present invention to provide an
economical and efficient apparatus for producing vacuum embossed
film.
The process of the present invention for vacuum embossing
thermoplastic film may be carried out by continuously advancing a
length of the film that is heated at least to its softening
temperature and applying the heated film to a portion of the
surface of an endless, seamless, perforated screen or belt
supported on a plurality of rotatable rolls. The perforated screen
or belt is advanced at the same rate as the heated film. A vacuum
is applied to at least a part of the undersurface of the perforated
screen or belt to pull the heated film into contact with the top
surface of the screen or belt to cause the film to assume the shape
of the pattern provided on the top surface of the screen or belt.
Heat is removed from the embossed film at a rate sufficient to
maintain the embossed film at a temperature sufficiently low enough
to cause the embossed film to substantially retain the pattern when
removed from the belt or screen. The film is continuously removed
from the screen or belt.
The apparatus of the present invention for vacuum embossing sheet
material includes a support roll, a drive roll, a support structure
for mounting the support roll and the drive roll for rotation, an
endless, seamless, flexible, porous screen mounted on the support
roll and the drive roll for rotation therewith, and a vacuum
assembly positioned between the pair of support rolls and engaging
a portion of the underside of the screen that extends between the
pair of support rolls.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective, schematic view of one embodiment of an
apparatus of the present invention suitable for carrying out the
process of the present invention;
FIG. 2 is a top plan view of a portion of a preferred embodiment of
the apparatus of the present invention with a portion of the
endless, seamless screen being cut away;
FIG. 3 is an elevational sectional view taken along lines 3--3 of
FIG. 2;
FIG. 4 is an end view of a portion of the apparatus of FIG. 3;
FIG. 5 is a cross-sectional view taken along lines 5--5 of FIG.
2;
FIG. 6 is a cross-sectional view taken along lines 6--6 of FIG. 2;
and
FIG. 7 is a partial cross-sectional view taken along lines 7--7 of
FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown a schematic view of an
apparatus of the present invention suitable for carryiing out the
process of the present invention which includes a conventional slot
die 10. It will be understood that slot die 10 is fed a plasticized
melt of a suitable polymer for forming a film (e.g., polyethylene,
polypropylene, polyvinyl chloride) and extrudes a sheet of film 11
in a horizontal direction. The sheet of film 11, while still hot
from extrusion, is applied to the top surface of an endless,
seamless, flexible, porous screen 22. Screen 22 is mounted on drive
roller 14 and on support roller 15, rollers 14 and 15 being
identical in construction. Spaced-apart cylindrical seal rolls
17--17 make rolling contact with the underside of screen 22. A
vacuum is applied by manifold 25 to the area lying between seal
rolls 17--17 and deckles 30--30 to pull the film 11 down onto
screen 22 to emboss the film. After the film leaves screen 22 it
next passes over chill roller 13 which is temperature-controlled to
cool the film, and from there it passes on to any suitable wind-up
roller 56, or the like for storing the film. Rollers 13, 14 and 15
are hollow inside and have hollow shafts 13a, 14a and 15a,
respectively, at each end thereof for circulating heating or
cooling fluid therethrough. It is understood that any suitable
means may be used for heating the film prior to the heated film
being received in the apparatus described hereinbefore in FIG. 1,
e.g., infrared lamps, hot air, passing the film over heated
rollers, or in contact with other suitable heated surfaces.
FIGS. 2-7 depict in greater detail a preferred embodiment of an
apparatus of the present invention for vacuum embossing film.
Referring now to FIGS. 2-6, the apparatus includes a generally
hollow, cylindrical drive roller 14 which drives screen 22 about
support rollers 15 and over seal rolls 17--17. Rollers 14 and 15
can be made from any suitable metal, e.g., steel, aluminum, bronze,
etc. Drive roller 14 is preferably covered with a suitable
elastomeric covering (not shown) such as, for example, a neoprene
or silicone rubber. As seen in FIGS. 2 and 4, drive roller 14 is
rotatably supported by hollow shaft members 14c and 14b received in
bearings 52 and 52a, which are attached to end plates 34 and 34a.
Shaft member 14c is connected by hollow nipple 29 to rotating union
36. Union 36 is connected by a supply conduit (not shown) to a
suitable supply of a heating or cooling fluid, e.g., water or oil,
and the shaft member 14b is connected to a discharge conduit and
union (not shown) for returning the fluid to the supply source.
Thus a heating or cooling fluid may flow through the hollow
interior 14f (see FIGS. 3 and 5) of drive roller 14, as indicated
by the arrows in FIG. 2.
Also located on shaft 14c is pulley 55. Pulley 55 is driven by any
suitable drive means such as a flexible V-belt, for example. Pulley
55 could also be replaced by a sprocket or any other conventional
drive means.
As can be seen in FIGS. 3 and 5, inner cylinders 14d and 15d are
contained with rollers 14 and 15, respectively. The inner cylinders
14d and 15d are sealed at each end by end plates 53--53 and are
connected to rollers 14 and 15 by supports 54, as shown in FIG. 3.
The inner cylinders 14d and 15d form a fluid space 14f and 15f
through which heating or cooling fluids flow as indicated by the
arrows in FIG. 5. More rapid and efficient heat transfer is
effected by this preferred design. However, inner cylinders 14d and
15d and end plates 53--53 could be eliminated if desired.
Support roller 15 is identical in construction, as previously
mentioned, to drive roller 14 and is supported by hollow shaft
members 15b-15c, respectively, which are received in bearings 19a
and 19 attached to end plates 34a and 34. Also, support roller 15
is hollow inside and is constructed in such a manner that heating
or coolant fluids such as oil or water may be forced therethrough
in the manner previously explained. As can be seen in FIGS. 2, 3
and 5, support roller 15 may be heated or cooled by supplying a
fluid through hollow shaft members 15c at one end and discharging
the fluid through hollow shaft members 15b at the other end.
Drive roller 14 is biased away from support roller 15 by tensioning
set screw 51, as can be seen in FIG. 4. An identical screw is
located at the opposite end of roller 14. The screws 51--51 urge
bearing assembly 52 and 52a outwardly to cause drive roller 14 to
place tension upon screen 22, thereby forcing screen 22 snugly
against the support roller 15, and seal rolls 17--17.
A vacuum assembly, designated generally by the numeral 23 is
positioned between support roller 15 and drive roller 14 to supply
vacuum to a portion of the underside of the top of screen 22. The
assembly includes a generally cylindrical manifold pipe 25, which
extends between end plates 34 and 34a and is attached thereto by
welding or other suitable means. Seal retainer strips 24 are
attached by bolts or other suitable means to each side edge of
manifold pipe 25 and project outwardly therefrom. A pair of spaced
apart seal rolls 17--17 are slidingly supported by manifold pipe 25
and strips 24--24. Rolls 17--17 make a sliding seal with retainer
strips 24--24 and manifold pipe 25. Seal rolls 17--17 are
preferably made from Teflon or other suitable plastic materials
having a low coefficient of friction.
Located between seal rolls 17--17 are deckles 30--30 which in turn
are threadably connected to deckle screws 31--31. Deckle screws
31--31 are connected by collars 21--21 to end plates 34 and 34a. By
turning deckle screws ends 31a--31a held in mounting bracket 35 and
end plate 34a, deckles 30--30 can be made to move inwardly and
outwardly along the shaft of the screw to adjust for various widths
or screen 22 or film 11. Each deckle 30, as can be seen in FIG. 3,
has a straight top edge and a curved bottom edge which make sliding
contact with the underside of screen 22 and manifold pipe 25,
respectively. The side edges of each deckle are generally
semi-circular in shape and fit flush against seal rolls 17--17 to
provide a sliding vacuum seal therebetween.
As can be seen in FIGS. 2 and 6, manifold pipe 25 has openings 27
therein through which air flows in the direction indicated by the
arrows when a vacuum is applied to manifold pipe 25. Vacuum is thus
applied to the underside of screen 22 which overlies the vacuum
chamber 50 defined by seal rolls 17--17. deckles 30--30 and
manifold pipe 25. When heated film 11 is carried by screen 22 over
seal rolls 17--17, the vacuum or low pressure existing in chamber
50 pulls the heated film 11 tightly against screen 22 to emboss the
film.
In one preferred embodiment of the present invention, a hydraulic
cylinder 63 is mounted on end plate 34a, as shown in FIGS. 2-5. The
purpose of hydraulic cylinder 63 is to prevent screen 22 from
sliding or walking off the end of drive roll 14 or support roll 15.
Hydraulic cylinder 63 accomplishes this purpose by moving the end
15b of drive roll 15 upward or downward, thereby "steering" or
causing screen 22 to move toward one end or the other of rolls 14
and 15.
As can be seen in FIG. 2, the hydraulic cylinder 63 is controlled
by an electric eye (photoelectric cell) 60 which is adapted to read
or "see" the edge 22a of screen 22. When electric eye 60 does not
"see" the edge 22a of screen 22, a signal is sent through line 62
to cylinder control 65, which in turn varies the hydraulic pressure
in hydraulic line 66 connected to hydraulic cylinder 63 to actuate
hydraulic cylinder 63. Hydraulic cylinder 63 causes steering unit
64 to move bearing 19a upward or downward. Preferably there are two
hydraulic cylinders 63--63, although only one is shown in the
drawings. The other hydraulic cylinder would be located on end
plate 34 at the opposite end 15c of roll 15 in the same manner in
which hydraulic cylinder 63 is connected to end plate 34a. The
other cylinder would move the end 15c of roller 15 in a direction
equal to and opposite to the direction in which cylinder 63 moves
end 15b, thus causing roll 15 to pivot about its center.
To carry out the process of the present invention a sheet of heated
thermoplastic film 11 is applied to the top surface of screen 22
lying between drive roller 14 and support roller 15. Screen 22 is
rotated by drive roller 14 thereby pulling film 11 over vacuum
chamber 50. Vacuum is applied to each end of the vacuum manifold
pipe 25, and a vacuum is created within the chamber 50 pulling the
heated film into firm embossing contact with the upper surface of
the embossing screen 22 to thereby transfer the pattern of the
embossing screen to the heated film 11. The heated film 11, after
passing over the vacuum space 50 is carried by screen 22 over drive
roll 14 and around chill roll 13 where the embossed film is rapidly
cooled to set the pattern of the film. Then, the cooled film is
removed and wound on a storage roll 56, or other suitable storage
means. The heated film 11 may be supplied by any of the means
described hereinbefore, i.e., by extrusion from a slot die mounted
directly above the embossing apparatus or by passing the film
through a heated air oven, or by heating the film by noncontacting
or contacting means, i.e., infrared heaters or heated rollers. The
film, after passing over vacuum chamber 50 may also be cooled by
circulating a cooling medium, e.g., refrigerated water, through
hollow drive roll 14. Optionally, the embossed film may also be
cooled by applying cold air to the top surface of the film after it
passes over the vacuum chamber. Screen 22 may be preheated to
enhance embossing of heated film 11 by circulating a heating medium
through hollow support roll 15.
Suitable thermoplastic materials may be embossed by the process of
the present invention, i.e., thin webs of from 0.25 mils up to as
thick as 10 mils. Exemplary thermoplastic materials suitable for
vacuum forming according to the present invention are polyethylene
and polyethylene copolymers, e.g., polyethylene-polypropylene
copolymers; polyvinyl chloride polymers and copolymers, e.g.,
polyvinyl chloride-polyvinyl acetate copolymers; polypropylene
homopolymers and copolymers; Saran films; Mylar films; polystyrene
films, and others.
While the use of refrigerated air and water contact have been
described as one form of cooling the embossing roll or screen, it
is understood that other forms may be used, i.e., internal fluid
cooling may be utilized by providing suitable conduits and passages
on the inside of the embossing roll. Also, conduits and passages
can be provided in both the drive roll 14, support rolls 15, and
chill roll 13 to remove heat from the embossing screen 22.
The foregoing embodiments are exemplary of the process and
apparatus for carrying out the present invention; however, many
variations of the invention may be made without departing from the
spirit and scope of the invention.
* * * * *